The specific aim of this proposal is to characterize age-related alterations in anterior pituitary lactotroph responses. A major focus of this work will be on the cell signal transduction mechanism of the lactotroph, specifically the hydrolysis of phosphatidyl-inositol-4,5- bisphosphate (PIP2). This produces an accumulation in inositol phosphates (IPs), notably inositol 1,4,5-triphosphate (IP3) which serves as an intracellular second messenger. Prolactin secretion and cell content, inositol phosphate accumulation and phospholipid metabolism will be determined in primary cultures derived from anterior pituitary glands from three different aged donor groups, i.e. young (3-4 months), mature (7-8 months) and old (22-24 months) male and female Sprague-Dawley rats. Cultures will be treated with secretagogues (TRH, Angiotensin II or neurotensin) which have been shown to increase prolactin release via PIP2 hydrolysis. The stimulatory activity of these secretagogues, as well as the ability of dopamine to inhibit these responses will be determined. In order to distinguish between possible differences in receptor binding characteristics of these secretagogues, the receptors will be by passed by administration of phorbol esters. The addition, the involvement of estrogen on pituitary responsiveness will be determined. This well be accomplished in two different ways. First, a number of female rats will be ovariectomized at 3-4 months and included as a separate group of pituitary donors for each of the older groups (i.e. mature and old). Second, the direct effects of estrogen on the pituitary will be assessed by adding it to the cultures. Lactotroph number will be quantified in all donor groups and all cells will be incubated in steroid free media. Aging produces a number of alterations in many physiologic functions. Significant changes occur in the endocrine system, including alterations in anterior pituitary secretory function, most notable, an increase in prolactin secretion. Aging is also clearly associated with an increase in pituitary adenomas (which involves the lactotroph population). Thus, alterations in the responsiveness of the anterior pituitary lactotroph may be an early marker of pituitary adenomas. It is important to understand the characteristic(s) and mechanism(s) associated with the aging process so that the relationship between normal aging and the pathogenesis of age- related diseases can be determined, especially taking into consideration the growing shift in demographics toward the elderly population in this country.